megaloblastic anemia

anemia

[ah-ne´me-ah]

a condition in which there is reduced delivery of oxygen to the tissues; it is not actually a disease but rather a symptom of any of numerous different disorders and other conditions. The World Health Organization has defined anemia as a hemoglobin concentration below 7.5 mmol/L (12 g/dL) in women and below 8.1 mmol/L (13 g/dL) in men.

Peripheral blood smears from a patient with megaloblastic anemia (left) and from a normal subject (right), both at the same magnification. The smear from the patient shows variation in the size and shape of erythrocytes and the presence of macro-ovalocytes. From Goldman and Bennett, 2000.

Some types of anemia are named for the factors causing them: poor diet (nutritional anemia), excessive blood loss (hemorrhagic anemia), congenital defects of hemoglobin (hypochromic anemia), exposure to industrial poisons, diseases of the bone marrow (aplastic anemia and hypoplastic anemia), or any other disorder that upsets the balance between blood loss through bleeding or destruction of blood cells and production of blood cells. Anemias can also be classified according to the morphologic characteristics of the erythrocytes, such as size (microcytic, macrocytic, and normocytic anemias) and color or hemoglobin concentration (hypochromic anemia). A type called hypochromic microcytic anemia is characterized by very small erythrocytes that have low hemoglobin concentration and hence poor coloration. Data used to identify anemia types include the erythrocyte indices: (1) mean corpuscular volume (MCV), the average erythrocyte volume; (2) mean corpuscular hemoglobin (MCH), the average amount of hemoglobin per erythrocyte; and (3) mean corpuscular hemoglobin concentration (MCHC), the average concentration of hemoglobin in erythrocytes. adj., adj ane´mic.

Symptoms. Mild degrees of anemia often cause only slight and vague symptoms, perhaps nothing more than easy fatigue or a lack of energy. As the condition progresses, more severe symptoms may be experienced, such as shortness of breath, pounding of the heart, and a rapid pulse; these are caused by the inability of anemic blood to supply the body tissues with enough oxygen. Pallor, particularly in the palms of the hands, the fingernails, and the conjunctiva (the lining of the eyelids), may also indicate anemia. In very advanced cases, swelling of the ankles and other evidence of heart failure may appear.

Common Causes of Anemia. Loss of Blood (Hemorrhagic Anemia): If there is massive bleeding from a wound or other lesion, the body may lose enough blood to cause severe and acute anemia, which is often accompanied by shock. Immediate transfusions are generally required to replace the lost blood. Chronic blood loss, such as excessive menstrual flow, or slow loss of blood from an ulcer or cancer of the gastrointestinal tract, may also lead to anemia. These anemias disappear when the cause has been found and corrected. To help the blood replenish itself, the health care provider may prescribe medicines containing iron, which is necessary to build hemoglobin, and foods with high iron content, such as kidney and navy beans, liver, spinach, and whole wheat bread.

Dietary Deficiencies and Abnormalities of Red Blood Cell Production (Nutritional Anemia, Aplastic Anemia, and Hypoplastic Anemia): Anemia may develop if the diet does not provide enough iron, protein, vitamin B12, and other vitamins and minerals needed in the production of hemoglobin and the formation of erythrocytes. The combination of poor diet and chronic loss of blood makes for particular susceptibility to severe anemia. Anemias associated with folic acid deficiency are very common.

Patient Care. Assessment of patients with some form of anemia will depend to some extent on the specific type of blood dyscrasia presented. In general, these patients do share some common problems requiring special assessment skills and interventions. Anemia can affect many different body systems

(see table). Although pallor of the skin is a sign of anemia, it is not the most reliable sign; many other factors can affect complexion and skin color. Jaundice of the skin and sclera can occur as a result of hemolysis and the release of bilirubin into the blood stream, where it eventually finds its way into the skin and mucous membranes. (See also jaundice.) Bleeding under the skin and bruises in response to the slightest trauma often are present in anemic and leukemic patients. A bluish tint to the skin (cyanosis) can indicate hypoxia due to inadequate numbers of oxygen-bearing erythrocytes.

Activity intolerance is a common problem for patients with anemia. Physical activity increases demand for oxygen, but if there are not enough circulating erythrocytes to provide sufficient oxygen, patients become physically weak and unable to engage in normal physical activity without experiencing profound fatigue. This can result in some degree of self-care deficit as the fatigue interferes with the patient's ability to carry on regular or enjoyable activities.

drug-induced hemolytic anemia (drug-induced immune hemolytic anemia) a form of immune hemolytic anemia induced by the taking of drugs, involving one of four different mechanisms:

Immune complex problems: Ingestion of any of a large number of drugs is followed by immunization and the formation of a soluble drug–anti-drug complex that adsorbs nonspecifically to the erythrocyte surface.

Drug absorption: Drugs bind firmly to erythrocyte membrane proteins, inducing the formation of specific antibodies; the drug most commonly associated with this mechanism is penicillin.

Membrane modification: A nonimmunologic mechanism whereby the drug involved is able to modify erythrocytes so that plasma proteins can bind to the membrane.

Autoantibody formation: Methyldopa (Aldomet) induces the production of autoantibodies that recognize erythrocyte antigens and are serologically indistinguishable from those seen in patients with warm autoimmune hemolytic anemia.

iron deficiency anemia a type of hypochromic microcytic anemia that results from the presence of greater demands on stored iron than can be met, usually because of chronic blood loss, dietary deficiency, or defective absorption; it is characterized by low or absent iron stores, low serum iron concentration, low transferrin saturation, elevated transferrin (total iron-binding capacity), and low hemoglobin concentration or hematocrit. Iron deficiency anemia is the most common nutritional disorder in the United States.

sideroachrestic anemia (sideroblastic anemia) any of a heterogenous group of acquired and hereditary anemias with diverse clinical manifestations, commonly characterized by large numbers of sideroblasts in the bone marrow, ineffective erythropoiesis, variable proportions of hypochromic erythrocytes in the peripheral blood, and usually increased levels of tissue iron.

spur cell anemia anemia in which the erythrocytes are acanthocytes (spur cells) and are destroyed prematurely, primarily in the spleen; it is an acquired form occurring in severe liver disease in which there is increased serum cholesterol and increased uptake of cholesterol into the erythrocyte membrane, causing the abnormal shape.

meg·a·lo·blas·tic a·ne·mi·a

any anemia in which there is a predominant number of megaloblastic erythroblasts, and relatively few normoblasts, among the hyperplastic erythroid cells in the bone marrow (as in pernicious anemia).

meg·a·lo·blas·tic a·ne·mi·a

Any anemia in which there is a predominant number of megaloblastic erythroblasts, and relatively few normoblasts, among the hyperplastic erythroid cells in the bone marrow (as in pernicious anemia).

meg·a·lo·blas·tic a·ne·mi·a

(meg'ă-lō-blast'ik ă-nē'mē-ă)

Anemia with a predominant number of megaloblastic erythroblasts and relatively few normoblasts, among hyperplastic erythroid cells in bone marrow.

anemia

a reduction below normal in the number or volume of erythrocytes or in the quantity of hemoglobin in the blood. Clinically it is manifested by weakness, exercise intolerance, hyperpnea which is only moderate, pallor of mucosae, tachycardia and a large increase in the intensity of the heart sounds. There are often accompanying signs related to the site of blood or hemoglobin loss.

aplastic anemia

a form of anemia generally unresponsive to specific antianemia therapy. It is often chronic, accompanied by granulocytopenia and thrombocytopenia, in which the bone marrow is usually acellular or hypoplastic. It may, however, be rapidly fatal. The term is actually all-inclusive and most probably encompasses several clinical syndromes. See pure red cell aplasia.

autoimmune hemolytic anemia

immune-mediated hemolytic anemia, which occurs in many species, particularly dogs, in which autoantibodies directed against red blood cells are produced. Different classes of immunoglobulins may be involved giving rise to differing clinical syndromes. Signs include pallor, lethargy, splenomegaly, and sometimes icterus, bilirubinuria and hemoglobinuria. There may also be an accompanying thrombocytopenia with bleeding tendencies. Diagnosis is based on a positive Coombs test.

an immune-mediated hemolytic anemia in which the antibody is maximally active at temperatures below 98.6°F (37°C). See also cold agglutinin disease.

cold (or cold water) anemia

a disease of cattle, especially calves, housed in warm barns and given near freezing water to drink. Dyspnea and the passage of red urine occur several hours after a large drink.

Coombs-positive anemia

immunoglobulin-mediated anemia that gives a positive reaction to Coombs tests, indicating the presence of immunoglobulins on the red cell surface. See also autoimmune hemolytic anemia (above), alloimmune hemolytic anemia of the newborn.

deficiency anemia

nutritional anemia.

drug-induced hemolytic anemia

some drugs such as quinine, quinidine, para-aminosalicylic acid, phenacetin, penicillin, insecticides, chlorpromazine, sulfonamides and dipyrone may be directly injurious to red cells or act to initiate an immune response in which red cells are destroyed.

familial nonspherocytic anemia of Basenji dogs

an inherited pyruvate kinase deficiency causes a hemolytic anemia with shortened red cell life span. In early stages, the disease is characterized by very active erythropoiesis but eventually, usually by the second or third year of life, a terminal myelofibrosis and osteosclerosis develops. The disease is inherited as an autosomal recessive trait.

hemolytic anemia resulting from oxidation of globin and formation of Heinz bodies, which are seen in blood smears as dark refractile intracytoplasmic bodies and stain with new methylene blue. Some common causes are ingestion of onions and plants in the Brassicaeae family, phenazopyridine, methylene blue and acetaminophen (paracetamol). Cats are particularly susceptible to Heinz body formation.

a nonregenerative, usually mild, anemia that occurs in association with malignancy or chronic infection. Although other causes of anemia such as hemolysis and blood loss may also occur with these conditions, there is altered iron metabolism with decreased serum iron and iron-binding capacity but with increased iron storage that results in decreased erythropoiesis.

anemia in which the erythrocytes are much larger than normal. The MCV (mean corpuscular volume) and MCH (mean corpuscular hemoglobin) are increased and the MCHC (mean corpuscular hemoglobin concentration) is normal.

megaloblastic anemia

anemia characterized by the presence of megaloblasts in the bone marrow and macrocytic erythrocytes. It occurs in vitamin B12, cobalt and folic acid deficiencies and in some myeloproliferative disorders in cats.

microangiopathic anemia

anemia due to fragmentation of erythrocytes in blood vessels whose endothelium has been badly damaged, usually by an infectious disease such as septicemias, disseminated intravascular coagulation and salmonellosis. Called also fragmentation anemia.

microcytic anemia

anemia characterized by decrease in size of the erythrocytes.

myelopathic anemia, myelophthisic anemia

anemia due to destruction or crowding out of hematopoietic tissues by space-occupying lesions, neoplasms and fibrosis.

nonregenerative anemia

one occurring without an appropriate erythropoietic response by the bone marrow.

normochromic anemia

that in which the hemoglobin content of the red cells as measured by the MCHC and MCH is within the normal range.

normocytic anemia

the anemia in which the red blood cells are normal in size.

nutritional anemia

anemia due to a deficiency of an essential substance in the diet, which may be caused by poor dietary intake or by malabsorption; called also deficiency anemia. See also pyridoxine, vitamin b12, folic acid, copper, iron.

parasitic anemia

hemorrhagic anemia due to blood loss caused by blood-sucking parasites such as fleas, hookworms and Haemonchus contortus.

associated with active erythropoiesis with increased numbers of reticulocytes, nucleated red blood cells, anisocytosis and polychromasia in the peripheral blood.

spur-cell anemia

anemia in which the red cells have a bizarre spiculated shape and are destroyed prematurely, primarily in the spleen; it is an acquired form occurring in severe liver disease, and represents an abnormality in the cholesterol content of the red cell membrane.

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